1. Field of the Invention
The present invention relates to a tunnel valve sensor and flux guide with improved flux transfer therebetween and, more particularly, to an electrically nonconductive magnetic oxide layer which is located between the tunnel valve sensor and the flux guide for permitting increased flux transfer therebetween.
2. Description of the Related Art
The heart of a computer is a magnetic disk drive which includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
An exemplary high performance read head employs a tunnel valve sensor for sensing the magnetic signal fields from the rotating magnetic disk. The sensor includes a nonmagnetic electrically nonconductive tunneling or barrier layer sandwiched between a ferromagnetic pinned layer and a ferromagnetic free layer. An antiferromagnetic pinning layer interfaces the pinned layer for pinning the magnetic moment of the pinned layer 90xc2x0 to an air bearing surface (ABS) wherein the ABS is an exposed surface of the sensor that faces the rotating disk. The tunnel valve sensor is located between ferromagnetic first and second shield layers. First and second leads, which may be the first and second shield layers, are connected to the tunnel valve sensor for conducting a tunneling current therethrough. The tunneling current is conducted perpendicular to the major film planes (CPP) of the sensor as contrasted to a spin valve sensor where a sense current is conducted parallel to the major film planes (CIP) of the spin valve sensor. A magnetic moment of the free layer is free to rotate upwardly and downwardly with respect to the ABS from a quiescent or zero bias point position in response to positive and negative magnetic signal fields from the rotating magnetic disk. The quiescent position of the magnetic moment of the free layer, which is parallel to the ABS, is when the tunneling current is conducted through the sensor without magnetic field signals from the rotating magnetic disk.
When the magnetic moments of the pinned and free layers are parallel with respect to one another the resistance of the tunnel valve sensor to the tunneling current (IS) is at a minimum and when their magnetic moments are antiparallel the resistance of the tunnel valve sensor to the tunneling current (IS) is at a maximum. Changes in resistance of the tunnel valve sensor are a function of cos xcex8, where xcex8 is the angle between the magnetic moments of the pinned and free layers. When the tunneling current (IS) is conducted through the tunnel valve sensor, resistance changes, due to signal fields from the rotating magnetic disk, cause potential changes that are detected and processed as playback signals. The sensitivity of the tunnel valve sensor is quantified as magnetoresistive coefficient dr/R where dr is the change in resistance of the tunnel valve sensor from minimum resistance (magnetic moments of free and pinned layers parallel) to maximum resistance (magnetic moments of the free and pinned layers antiparallel) and R is the resistance of the tunnel valve sensor at minimum resistance. The dr/R of a tunnel valve sensor can be on the order of 40% as compared to 10% for a spin valve sensor.
The first and second shield layers may engage the bottom and the top respectively of the tunnel valve sensor so that the first and second shield layers serve as leads for conducting the tunneling current IS through the tunnel valve sensor perpendicular to the major planes of the layers of the tunnel valve sensor. The tunnel valve sensor has first and second side surfaces which intersect the ABS. First and second hard bias layers abut the first and second side surfaces respectively of the tunnel valve sensor for longitudinally biasing the free layer. This longitudinal biasing also helps to maintain the magnetic moment of the free layer parallel to the ABS when the read head is in the quiescent condition.
Magnetic head assemblies, wherein each magnetic head assembly includes a read head and a write head combination, are constructed in rows and columns on a wafer. After completion at the wafer level, the wafer is diced into rows of magnetic head assemblies and each row is lapped by a grinding process to lap the row to a predetermined air bearing surface (ABS). In a typical tunnel valve read head all of the layers are exposed at the ABS, namely first edges of each of the first shield layer, the seed layer, the free layer, the barrier layer, the pinned layer, the pinning layer and the second shield layer. Opposite edges of these layers are recessed in the head. The barrier layer is a very thin layer, on the order of 20 xc3x85, which places the free and pinned layers very close to one another at the ABS. When a row of magnetic head assemblies is lapped there is a high risk of magnetic material from the free and pinned layers being smeared across the barrier layer at the ABS to cause a short therebetween. Accordingly, there is a strong-felt need to construct magnetic head assemblies with tunnel valve heads without the risk of shorting between the free and pinned layers at the ABS due to lapping.
A scheme for preventing shorts across the barrier layer of the tunnel valve sensor is to recess the tunnel valve sensor within the head and provide a flux guide between the ABS and the sensor for guiding flux signals from the rotating magnetic disk. In this scheme a tunnel valve sensor has front and back surfaces which are recessed from the ABS and the flux guide has a ferromagnetic flux guide body with front and back surfaces wherein the front surface forms a portion of the ABS and the back surface is magnetically coupled to the tunnel valve sensor. Located between and interfacing each of the back surface of the flux guide body and the front surface of the tunnel valve sensor is an electrically nonconductive insulation layer which is very thin, on the order of 8 xc3x85, in order to permit flux transfer from the flux guide to the tunnel valve sensor. Additional insulation layers are located between the top and bottom surfaces of the flux guide and the shield layers to electrically insulate the flux guide from the shield layers when the shield layers are employed for conducting the tunneling current (IT) to the tunnel valve sensor. These insulation layers can be made sufficiently thick so that when a row of magnetic head assemblies is lapped, as discussed hereinabove, there is no or minimum risk of conductive material being smeared between the layers to cause a short. The flux guide also permits a very narrow track width to be obtained by fabricating the flux guide with a narrow width at the ABS and increasing the width of the flux guide as it extends toward the tunnel valve sensor. With this arrangement the tunnel valve sensor can be maintained wide for reducing the resistance of the tunnel valve sensor to the tunneling current (IT). Accordingly, the tunneling current (IT) can be then increased for improving the signal response of the tunnel valve sensor.
A typical material employed for the insulation layer between the back surface of the flux guide and the front surface of the tunnel valve sensor is aluminum oxide (Al2O3). While this insulation layer is maintained relatively thin, as discussed hereinabove, a significant amount of flux cannot be transferred between the flux guide and the spin valve sensor because of the characteristics of aluminum oxide. Accordingly, there is a strong-felt need to improve the performance of the tunnel valve sensor and flux guide arrangement by improving the amount of flux transferred from the flux guide to the tunnel valve sensor.
The present invention provides an electrically nonconductive insulation layer between the back surface of the flux guide and the front surface of the tunnel valve sensor which permits improved flux transfer between the flux guide and the tunnel valve sensor. This is accomplished by making the insulation layer from a magnetic oxide. Suitable magnetic oxides are selected from the group consisting of nickel iron oxide (NiFeO), cobalt oxide (CoO), nickel oxide (NiO), cobalt iron oxide (CoFeO), nickel iron cobalt oxide (NiFeCoO) and iron hafnium oxide (FeHfO). In a preferred embodiment the insulation layer between the flux guide and the first shield layer is also a magnetic oxide so that this layer and the layer between the flux guide and the spin valve sensor can be sputter deposited simultaneously.
An object of the present invention is to provide a tunnel valve sensor and flux guide with improved flux transfer therebetween.
Another object is to provide an insulation layer between the flux guide and the tunnel valve sensor which permits improved flux transfer from the flux guide to the tunnel valve sensor.
A further object is to provide methods of making the aforementioned tunnel valve sensor and flux guide arrangements.
Other objects and attendant advantages of the invention will be appreciated upon reading the following description taken together with the accompanying drawings.